Synthesis and Structural Elucidation of a Pyranomorphinan Opioid and in Vitro Studies

During optimization of the synthesis of the mixed μ opioid agonist/δ opioid antagonist 5-(hydroxy­methyl)­oxy­morphone (UMB425) for scale-up, it was unexpectedly discovered that the 4,5-epoxy bridge underwent rearrangement on treatment with boron tribromide (BBr3) to yield a novel opioid with a little-studied pyranomorphinan skeleton. This finding opens the pyranomorphinans for further investigations of their pharmacological profiles and represents a novel drug class with the dual profile (μ vs δ) predicted to yield lower tolerance and dependence. The structure was assigned with the help of 1D, 2D NMR and the X-ray crystal structure.